456 Mr. J. B. B. Burke on the 



adjoining wires, and the bulb. But this was got over by using 

 large screens. The connexions between cd and the electro- 

 meter were by insulated brass rods surrounded by tubes put 

 to earth. One volt corresponded to 50 divisions of the scale. 



Before sending the discharge through the bulb, the two 

 pairs of quadrants were connected and then disconnected. 

 As soon as the discharge passed, the electrode d gradually 

 acquired a charge of the same sign as that on c, whether 

 this was positive or negative ; and on reversing the con- 

 nexions with the electrodes, so that c was insulated and 

 connected to one pair of quadrants of the electrometer and d 

 to one pole of the battery, a similar effect was produced. The 

 conductivity lasts for some seconds after the discharge has 

 stopped passing in the bulb. 



It is very remarkable that putting on a large E.M.F. of 

 320 volts between ab does not stop or diminish the con- 

 ductivity as measured between cd. 



The conductivity between cd is not exactly of the same 

 magnitude, according as the E.M.F. is along cd or dc. 

 When c is the insulated electrode it always receives a negative 

 charge; and this would affect the rate at which it would 

 take up the ions of the opposite charge to those taken up by d. 



There is a maximum potential which the insulated electrode 

 will attain in virtue of the conductivity; and if initially its 

 potential is greater than this amount, it falls rapidly until the 

 potential in question is reached, depending upon the potential 

 of the other electrode. 



Thus with air at a pressure of 0'235 mm. and c charged 

 positively to a potential of 8 volts a positive charge is rapidly 

 acquired by d up to 285 divisions o£ the scale. If now the 

 insulated electrode d be charged to the same potential as c, 

 the reading on the scale is 410 ; but when sparking com- 

 mences and the glow reaches the electrodes, the potential of d 

 rapidly falls to 285. 



When c is negative, d acquires a negative charge corre- 

 sponding to —100. If while d is at —100, c is changed from 

 the negative to the positive pole of the battery and the sparks 

 sent through the bulb, the positive potential corresponding 

 to — 285 divisions of the scale is rapidly obtained after a few 

 sparks. 



(14) The fact that the glow can diffuse through narrow 

 metal tubing and pass between the wire-gauze electrodes 

 charged to a high potential, or between two such electrodes 

 close together with an electromotive force between them, 

 without having its velocity or intensity altered, nor the con- 

 ductivity lower down the tube sensibly diminished, seems to 



